The proposed investigation is in two parts. The first deals with the colors of photopigment housed in different receptors and the receptor mosaic. The aim is to develop techniques of photographing visual pigments in situ in dark-adapted retinas in color. Since photopigments bleach in light, a very fast flash techniques of photography would work. The color of the photoreceptor would then be one of the means for characterizing the receptor mosaic. Emphasis will be to photograph areas of high density of photoreceptors such the linea centralis, or area centralis, or fovea. For those cases where photographing the retina is not feasible, our objective is to develop a computer program for calculating the color of visual pigment in photoreceptors and then paint an appropriate montage. Rana pipiens is chosen as the animal model for the experimentation. The experiments proposed are appropriate for undergraduate research. The second part of the proposal deals with investigating the characteristics of the visual system in estuarine fish (e.g., striped bass, menhaden, yellow perch) inhabiting the Chesapeake Bay. A structure-function correlation will be established. The structure will be studied with light microscopy with Nomaraski optics. The receptor mosaic and rod/cone ratios will be determined. The physiologic investigation includes determinations of electroretinographic visual spectral sensitivity (by criterion and flicker photometry methods), critical flicker fusion frequency, and scotopic and photopic threshold. In situ MSP will be conducted to determine the absorption spectra of the photopigments present in the fish photoreceptors at different stages in the life-cycle, from juveniles to mature adults. The studies of the fish visual system are suitable for thesis research at the graduate level.